The invention relates to an at least substantially metallic cylinder head gasket.
The metallic cylinder head gaskets currently in use have a gasket plate which is essentially formed by a single sheet metal layer consisting of sheet spring steel or of several layers of sheet steel superimposed on one another, with at least one layer thereof consisting of sheet spring steel. Around the combustion chamber openings and fluid openings (the latter for coolant and/or engine oil) that are to be sealed off, the layer of sheet steel or at least one of the layers of sheet steel has stamped sealing beads which are capable of undergoing spring-elastic deformation in a direction perpendicular to the gasket plate so as to maintain the pressure required for the sealing effect around the openings of the cylinder head gasket that are to be sealed off, when, upon tightening the cylinder head screws and during operation of the engine, the engine component sealing surfaces of cylinder head and engine block, which are flat prior to installation of the gasket, undergo deformation and no longer constitute flat surfaces. Such metallic cylinder head gaskets are disclosed, for example, in U.S. Pat. No. 5,582,415.
A completely different operational principle of a substantially metallic cylinder head gasket is disclosed in EP-0 485 693-B1 or the corresponding U.S. Pat. No. 5,391,333. According to this, a cylinder head gasket comprises a one-piece metallic gasket plate, whose main surfaces facing the engine component sealing surfaces have a specific topography with its form based on the following consideration: the engine block (crankcase) and the cylinder head cannot be regarded as absolutely rigid components for the function of a cylinder head gasket. Rather, the tightening of the cylinder head screws and the changing gas pressures in the combustion chambers during operation of the engine cause sagging of these engine components, i.e., result in the sealing gap delimited by the engine component sealing surfaces and accommodating the cylinder head gasket for sealing it not maintaining the form of a thin plane-parallel plate. However, the locally varying component rigidity of these two engine components in areas adjoining their sealing surfaces also influences the topography of the engine component sealing surfaces delimiting the sealing gap during operation of the engine. The shape of the gasket plate of the cylinder head gasket according to EP-0 485 693-B1 is based on the basic concept of adapting the shape of the gasket plate of the cylinder head gasket in the areas effective for the sealing to the topography of the engine component sealing surfaces, as prevails after the tightening of the cylinder head screws, i.e., after installation of the cylinder head gasket, and of not allowing the elastic component deformations required for maintaining the sealing during operation of the engine to occur on or in the cylinder head gasket but instead on or in the engine components engine block and cylinder head, so that the gasket plate of the cylinder head gasket can be made from a material which is stable when tightening the cylinder head screws and during operation of the engine, i.e., is not deformable in its thickness. This basic concept underlying the design of a cylinder head gasket does, of course, not exclude providing the gasket plate with a plastic coating, for example, for the purpose of so-called microsealing, which can be adapted to surface roughnesses of the engine component sealing surfaces.
There are cases where cylinder head gaskets are used, in which a gasket with a topographically designed gasket plate which at least in its areas serving for sealing is to be regarded as rigid does not produce optimum results: above all, modern diesel engines of lightweight construction cannot be reliably sealed with a cylinder head gasket designed strictly according to the teaching of EP-0 485 693-B1 with both a cold and a warm engine, for the following reason: if the cylinder head gasket is designed so that the engine is tight in the cold state, the cylinder pipes (the wall areas enclosing the combustion chambers in the engine block) expanding to the greatest extent in a direction perpendicular to the sealing gap between cylinder head and engine block in the course of reaching the operating temperature of the engine lead to the cylinder head being raised and at a spacing from the combustion chamber openings of the cylinder head gasket being lifted off the latter, with the result that the lubricating oil and coolant passages passing through the cylinder head gasket become untight. In addition, the very different temperature expansion coefficients of the materials of engine block (usually gray cast iron) and cylinder head (light metal alloys) in such engines with the unavoidable changes in temperature of the engine during operation of the engine lead to relatively large sliding movements of the engine component sealing surfaces of cylinder head and engine block relative to one another and relative to the cylinder head gasket in the plane of the sealing gap to be sealed by the cylinder head gasket and thus to detrimental wear occurring, above all, on the cylinder head.
A cylinder head gasket is now proposed by the invention, which eliminates the sealing problem described hereinabove and nevertheless has the major advantages of a cylinder head gasket with a single-layered metallic gasket plate with sealing areas which are stable, i.e. not deformable in their height, in accordance with EP-0 485 693-B1, around the combustion chamber openings of the gasket plate.